docs: def add_point_feature(self, resnum, feat_type=None, feat_id=None, qualifiers=None):
          """Add a feature to the features list describing a single residue.
  
          Args:
              resnum (int): Protein sequence residue number
              feat_type (str, optional): Optional description of the feature type (ie. 'catalytic residue')
              feat_id (str, optional): Optional ID of the feature type (ie. 'TM1')
  
          """
          if self.feature_file:
              raise ValueError('Feature file associated with sequence, please remove file association to append '
                               'additional features.')
  
          if not feat_type:
              feat_type = 'Manually added protein sequence single residue feature'
          newfeat = SeqFeature(location=FeatureLocation(ExactPosition(resnum-1), ExactPosition(resnum)),
                               type=feat_type,
                               id=feat_id,
                               qualifiers=qualifiers)
  
          self.features.append(newfeat)